Hidden indicia have been used in the past in conjunction with photographic processes and the like in which developers are used to expose or develop the indicia thereby providing a message which appears on a carrier. In the use of many prior art systems, expensive or caustic developers must be used in order to develop the hidden indicia into a readily visible display. This is often undesirable, particularly where the indicia is to be used in conjunction with small children or in a mass producing system in which an inexpensive developer is required or with food where toxicity must be avoided. Expensive and dangerous systems are avoided by the present invention which utilizes water as an activator.